Image forming apparatus

ABSTRACT

An image forming apparatus includes: an image carrying unit; a unit-to-be-moved; a pulse motor; a moving mechanism including a rotatable member provided with a member-to-be-detected; a detecting portion; an executing portion; and a controller for causing the executing portion to execute a first stop mode on the basis of detection of the detecting portion when the unit-to-be-moved is changed in position from the second or third position to the first position and to execute a second stop mode on the basis of a pulse number of a driving signal when the unit-to-be-moved is changed in position from the first or third position to the second position and when the unit-to-be-moved is changed in position from the first or second position to the third position, and for making the change at least between the second and third positions by only unidirectional rotation of the pulse motor.

FIELD OF THE INVENTION AND RELATED ART

The present invention relates to an image forming apparatus, such as aprinter, a facsimile machine or a copying machine, using anelectrophotographic type or an electrostatic recording type.

Various conventional image forming apparatuses employing an imageforming process of the electrophotographic type or the electrostaticrecording type exist, and in these image forming apparatuses, there is atype as shown below. As an example thereof, there is an intermediarytransfer tandem type in which a plurality of process cartridges arearranged in line along a rotational direction of a rotatably stretchedintermediary transfer belt and a color image is formed via theintermediary transfer belt.

In the image forming apparatus of such an intermediary transfer tandemtype, there is an image forming apparatus in which an endlessintermediary transfer belt is stretched by a plurality of stretchingrotates including a driving roller. In this image forming apparatus, aprimary-transfer portion is formed between a photosensitive drum and aprimary-transfer roller which are provided opposed to each other at aposition, between the two stretching rollers, where the intermediarytransfer belt is sandwiched between the photosensitive drum and theprimary-transfer roller. Further, a secondary-transfer portion is formedbetween an inner secondary-transfer roller and an outersecondary-transfer roller, capable of performing acontact-and-separation operation relative to the innersecondary-transfer roller, which are provided opposed to each other soas to sandwich the intermediary transfer belt in a downstream side of arotational direction of the intermediary transfer belt.

In a full-color image forming apparatus of the intermediary transfertandem type, there is a constitution in which image formation iseffected using, e.g., four colors (yellow, magenta, cyan, black) and inwhich an operation in a monochromatic mode (Bk single-color mode) inwhich the image formation for only black (Bk) is effected is executable.In the case where a monochromatic mode image is formed by thisconstitution, rotation of photosensitive drums and developing devices,for yellow, magenta and cyan, which are not required to be operated isstopped, so that deterioration of the photosensitive drums anddevelopers is prevented and thus a running cost of the apparatus can bereduced.

In an operation in a full-color mode in which a full-color image isformed by using the photosensitive drums for all the four colors, theintermediary transfer belt is contacted to all the operatingphotosensitive drums for yellow, magenta, cyan and black. On the otherhand, in the operation in the monochromatic mode, the intermediarytransfer belt is temporarily separated (spaced) from the photosensitivedrums, for yellow, magnet and cyan, which are stopped. Further, duringmaintenance of a transfer unit including the intermediary transfer beltor the like and during transportation or the like of the image formingapparatus, also an operation in an all separation mode in which theintermediary transfer belt is separated (spaced) from all thephotosensitive drums, for yellow, magenta, cyan and black, which arestopped exists.

In such an image forming apparatus, as disclosed in Japanese Laid-OpenPatent Application (JP-A) 2010-282124, there is a constitution in whicha plurality of primary-transfer rollers and a plurality of stretchingrollers are supported by a fixed frame for supporting the plurality ofstretching rollers via a movable frame which is swingable and in whichthe movable frame is selectively swung. As a result, the operation inthe monochromatic mode is carried out after the primary-transfer rollersfor the colors other than black are separated from the correspondingphotosensitive drums, and the operation in the full-color mode iscarried out after all the primary-transfer rollers are moved toward thecorresponding photosensitive drums. Alternatively, also an image formingapparatus capable of executing an operation in an all separation mode,as another mode, in which all the primary-transfer rollers are separatedfrom the corresponding photosensitive drums during the maintenance andduring the transportation of the apparatus has been known.

On the other hand, also an image forming apparatus operable in aseparation mode in which the outer secondary-transfer roller isseparated from the intermediary transfer belt when the toner image doesnot exist on the intermediary transfer belt exists. In this imageforming apparatus, by preventing contamination and deterioration of thesecondary-transfer roller by the toner deposited on the intermediarytransfer belt in a region other than an image forming region, servicelife extension is intended. In this apparatus, there is also aconstitution in which during maintenance of a secondary-transfer unitincluding the outer secondary-transfer roller or the like and during theapparatus transportation, the outer secondary-transfer roller is furtherlargely spaced. Also in such an apparatus, a control position isswitched among a position of an operation in a contact mode in which theouter secondary-transfer roller is contacted to the intermediarytransfer belt during the image formation, a position of an operation ina separation mode in which the outer secondary-transfer roller isseparated from the intermediary transfer belt and a stand-by positionbetween these positions.

In this way, in a constitution having three modes with respect to acontact secondary-transfer of the primary-transfer rollers or thesecondary-transfer roller, a constitution such that the three modes areswitched by a single sensor and a single motor in order to reduce a userstress by further shortening of a switching time and to reduce anapparatus cost. In the image forming apparatus operable in the threemodes, as a constitution applied to a developing roller or the likewithout being limited to the transfer roller as disclosed in JP-A2006-323235, there is a constitution in which the position of theoperation in the separation mode is set at the stand-by position and inwhich the three modes are switched by the single sensor and the singlemotor.

However, in the image forming apparatus disclosed in JP-A 2010-282124,the stand-by position is the separation mode position, and thereforewhen the monochromatic mode and the full-color mode are repetitivelyswitched by normal rotation and reverse rotation of the motor, there isa liability that an error is accumulated. In this case, there is apossibility that a problem such that the apparatus cannot be stoppedfinally in the operation in a desired mode and thus the toner image isnot transferred or a lifetime is shortened arises. In order to avoidthis problem, it would be also considered that a rotational direction ofthe motor is always set unidirectionally, but in this case, a timerequired for switching becomes long. In this way, the switch of the modewith reliability and the short switch time were in a trade-offrelationship.

Further, also in the image forming apparatus disclosed in JP-A2006-323235, in order to return the position to the stand-by positionduring power-on of the apparatus or during an initializing operation forseparation switch, there is a need to always once detect all of flags.For that reason, the motor has to be rotated once every time, so thatthere was a problem such that a rising time of the apparatus becomeslong.

As described above, when the mode switching time or the apparatus risingtime becomes large, downtime of the apparatus becomes long, so thatthere is a possibility that a new problem of stress applied to a user ora short lifetime of the apparatus occurs.

SUMMARY OF THE INVENTION

According to an aspect of the present invention, there is provided animage forming apparatus comprising: an image carrying unit for carryinga toner image; a unit-to-be-moved for being moved so as to change aposition thereof relative to the image carrying unit; a pulse motorrotatable bi-directionally on the basis of a pulse number of a drivingsignal; a moving mechanism, including a rotatable member rotatablebi-directionally in synchronism with rotation of the pulse motor, formoving the unit-to-be-moved so that predetermined three different phasesof the rotatable member corresponds to first to third positions of theunit-to-be-moved, respectively, wherein the rotatable member is providedwith a member-to-be-detected correspondingly to a specific phase range;a detecting portion provided at a position where themember-to-be-detected is detected when the unit-to-be-moved is in thefirst position; an executing portion for executing, when theunit-to-be-moved is changed in position from one of the first to thirdpositions to another position, an operation in a first stop mode inwhich the rotatable member is stopped on the basis of detection of thedetecting portion and an operation in a second mode in which therotatable member is stopped on the basis of the pulse number of thedriving signal sent to the pulse motor; and a controller for causing theexecuting portion to execute the operation in the first stop mode whenthe unit-to-be-moved is changed in position from the second or thirdposition to the first position and to execute the operation in thesecond stop mode when the unit-to-be-moved is changed in position fromthe first or third position to the second position and when theunit-to-be-moved is changed in position from the first or secondposition to the third position, and for making the change at leastbetween the second and third positions by only unidirectional rotationof the pulse motor.

These and other objects, features and advantages of the presentinvention will become more apparent upon a consideration of thefollowing description of the preferred embodiments of the presentinvention taken in conjunction with the accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a sectional view showing a general structure of an imageforming apparatus according to First Embodiment of the presentinvention.

FIG. 2 is a perspective view showing a mounting and dismountingdirection of an intermediary transfer belt unit in First Embodiment.

FIGS. 3, 4 and 5 are schematic perspective views showing aprimary-transfer contact-and-separation mechanism in First Embodiment.

FIG. 6, (a) and (b) are front views showing a cam member duringfull-color image formation in First Embodiment.

In FIG. 7, (a) and (b) are front views showing the cam member duringmonochromatic image formation in First Embodiment.

In FIG. 8, (a) and (b) are front views showing the cam member during allseparation in First Embodiment.

FIG. 9 is a schematic perspective view showing a drive transmittingdevice in First Embodiment.

FIG. 10 is a schematic perspective view showing a driven gear train inFirst Embodiment.

In FIG. 11, (a) to (d) are schematic views showing a coupling portion.

In FIG. 12, (a) to (c) are schematic views showing a state of thecoupling portion before disengagement of the intermediary transfer beltunit starts.

In FIG. 13, (a) to (c) are schematic views showing a contact-eliminatedstate between first and second engaging portions of the couplingportion.

In FIG. 14, (a) to (c) are schematic views showing a distance betweenrotation shafts of the coupling portions.

FIG. 15 is a schematic view showing an operation of a flag portion and asensor of the drive transmitting device in First Embodiment.

FIG. 16 is a schematic view showing another operation of the flagportion and the sensor of the drive transmitting device in FirstEmbodiment.

FIG. 17 is a schematic view of a state, as seen in an arrow U directionof FIG. 9, showing a rotational position of a flag gear in FirstEmbodiment.

FIG. 18 is a flowchart showing a control flow of switching from afull-color mode to a monochromatic mode.

FIG. 19 is a flowchart showing a control flow of switching from themonochromatic mode to the full-color mode.

FIG. 20 is a flowchart showing a control flow of switching from thefull-color mode to an all separation mode.

In FIG. 21, (a) and (b) are illustrations showing a constitution inComparison Example.

In FIG. 22, (a) is a sectional view of a state in which an outersecondary-transfer roller is contacted to a driving roller in SecondEmbodiment of the present invention, and (b) is a sectional view of astate in which the outer secondary-transfer roller is moved to astand-by position.

FIG. 23 is a sectional view of a state in which the outersecondary-transfer roller is moved to a separation position in SecondEmbodiment.

DESCRIPTION OF THE EMBODIMENTS First Embodiment

With reference to the drawings, embodiments according to the presentinvention will be specifically described below. Throughout the drawings,the same reference numerals or symbols represent the same orcorresponding portions. Incidentally, a principal part relating toformation and transfer of a toner image is principally described, butthe present invention can be carried out in various uses, such as aprinter, various printing machines, a copying machine and amulti-function machine, by adding necessary equipment, device and casingstructure.

Image Forming Apparatus

First, with reference to FIG. 1, an image forming apparatus in thisembodiment will be described. FIG. 1 is a schematic sectional viewshowing a schematic structure of an image forming apparatus 50, such asa full-color printer, of a tandem type and an intermediary transfertype.

As shown in FIG. 1, the image forming apparatus 50 includes an apparatusmain assembly 50 a. In the apparatus main assembly 50 a, a controller45, including ROM, RAM and CPU, for controlling respective portions ofthe image forming apparatus 50 is incorporated. To this controller 45, aprimary-transfer contact-and-separation mechanism 30 connected via adriving motor 41 described later and an unshown another drivingmechanism and the like are connected.

In the image forming apparatus 50, toner image formation is effected byphotosensitive drums 1 (1 a-1 d) as image bearing members(photosensitive members), charging rollers 2 (2 a-2 d) as chargingmeans, an exposure unit 3, developing units 4 (4 a-4 d) as developingmeans, and the like.

In the following, e.g., in the case where the photosensitive drums areindividually described, the photosensitive drums are individuallydescribed, the photosensitive drums are represented by thephotosensitive drums 1 a, 1 b, 1 c, 1 d and in the case where thephotosensitive drums are collectively described, the photosensitivedrums are represented by the photosensitive drum 1. This is true forother portions.

Toner Image Forming Process

At a periphery of the photosensitive drums 1 a, 1 b, 1 c, 1 d, alongrespective rotational directions, the charging rollers 2 a, 2 b, 2 c, 2d for electrically charging surfaces of the photosensitive drumsuniformly and the exposure unit 3 for forming an electrostatic latentimage on each photosensitive drum by irradiating each photosensitivedrum with a laser beam on the basis of image information in the listedorder. The developing units 4 a, 4 b, 4 c, 4 d and primary-transferrollers 12 a, 12 b, 12 c, 12 d for primary-transferring the toner imagesfrom the photosensitive drums onto an intermediary transfer belt 12 e asa member-to-be-moved are provided. The developing units 4 a-4 dvisualize the electrostatic latent images into the toner images bydepositing toners on the electrostatic latent images formed on thephotosensitive drums. Further, cleaning means 8 (8 a, 8 b, 8 c, 8 d) forremoving transfer residual toners remaining on the photosensitive drumsurfaces after the primary-transfer, and the like means are provided.

The primary-transfer rollers 12 a-12 d are constituted so that theintermediary transfer belt 12 e as the member-to-be-moved is movable todifferent three positions (arrangements) relative to the photosensitivedrums (image bearing members) 1 a-1 d by drive the driving motor 41consisting of a pulse motor such as a stepping motor. The driving motor41 consisting of the pulse motor is constituted so as to be capable ofbeing rotated and driven by-directionally on the basis of a pulse numberof a driving signal. The above-mentioned positions or the like will bedescribed later.

The charging rollers 2 and the cleaning means 8 are assembled into aunit as cleaning units 5 (5 a, 5 b, 5 c, 5 d). The photosensitive drums1, the cleaning units 5 and the developing units 4 and the like areintegrally assembled into cartridges as process cartridges 7 (7 a, 7 b,7 c, 7 d).

Each of the process cartridges 7 a-7 d is constituted so as to beinsertable into and pulled out from (detachably mountable to) theapparatus main assembly 50 a. These four process cartridges 7 a-7 d aredifferent in that images different in color are formed using toners ofyellow (Y), magenta (M), cyan (C) and black (Bk), but have the samebasic structure.

The developing units 4 a, 4 b, 4 c, 4 d include developing rollers 24 a,24 b, 24 c, 24 d, developer applying rollers 25 a, 25 b, 25 c and 25 d,and toner containers (not shown). In the toner containers, the toners ofthe colors of yellow (Y), magenta (M), cyan (C) and black (Bk),respectively, are accommodated.

The cleaning units 5 a, 5 b, 5 c, 5 d include the photosensitive drums(image bearing members, photosensitive members) 1 a, 1 b, 1 c, 1 d, thecharging rollers 2 a, 2 b, 2 c, 2 d, the cleaning means 8 a, 8 b, 8 cand 8 d, are transfer residual toner collecting containers (not shown).

Each of the photosensitive drums 1 a-1 d is constituted by applying alayer of an organic photoconductor (OPC) onto an outer peripheralsurface of an aluminum cylinder, and is rotatably supported at endportions thereof. At one of the end portions of each of thephotosensitive drums 1 a-1 d, when a driving force is transmitted toeach of the photosensitive drums 1 a-1 d from the driving motor (notshown), each of the photosensitive drums 1 a-1 d is rotationally drivenin the clockwise direction indicated by an arrow in FIG. 1.

Each of the charging rollers 2 a-2 d is formed with an electroconductiveroller in a roller shape. This charging roller is contacted to thesurface of associated one of the photosensitive drums 1 a-1 d and issupplied with a charging voltage from a power source circuit (notshown), so that the surface of each of the photosensitive drums 1 a-1 dis uniformly charged. Further, the exposure unit 3 is disposed below theprocess cartridges 7 a-7 d with respect to a vertical direction, andsubjects each of the photosensitive drums 1 a, 1 b, 1 c, 1 d to exposureto light on the basis of an image signal.

The developing rollers 24 a-24 d are disposed adjacently to the surfacesof the photosensitive drums 1 a-1 d, and are rotationally driven by adriving portion (not shown) and are supplied with a voltage, whereby theelectrostatic images are developed on the surfaces of the photosensitivedrum 1 a-1 d.

By the above constitution, the toner images of yellow (Y), magenta (M),cyan (C) and black (Bk) are formed on the surfaces of the photosensitivedrums 1 a-1 d, respectively. The toner images formed on the surfaces ofthe photosensitive drums 1 a-1 d are primary-transferred successivelyonto the intermediary transfer belt (member-to-be-moved) 12 e.Thereafter, the toners remaining on the photosensitive drums 1 a-1 d areremoved by the corresponding cleaning means 8 c-8 d, respectively, andthen are collected in transfer residual toner collecting containers (notshown) in the cleaning units 5 a-5 d.

Transfer Onto Recording Material and Fixing Process

At a lower portion of the apparatus main assembly 50 a, a paper feedingcassette 11 for accommodating a recording material S is provided. Thepaper feeding cassette 11 is mounted so as to be pullable out in afrontward direction (toward a left side of the apparatus main assembly50 a in FIG. 1) of the apparatus main assembly 50 a. A useraccommodates, stacks and sets the recording material S in the paperfeeding cassette 11 out of the apparatus main assembly 50 a, and theninserts the paper feeding cassette 11 into the apparatus main assembly50 a, so that it is possible to supply the recording material S.

During the image formation, the recording material S is fed out from thepaper feeding cassette 11 by a paper feeding roller 9 and then is fed toa registration roller pair 17 via a feeding roller pair 10. A paperfeeding device 13 includes a semilunar paper feeding roller 9, aseparating means 23 and the feeding roller pair 10 for nipping andfeeding the recording material S. The registration roller pair 10 isprovided downstream of the feeding roller pair 10.

The paper feeding roller 9 is provided so as to be contactable to therecording material S accommodated in the paper feeding cassette 11, andis rotated by a controller 45 at predetermined control timing, thussending the recording material S. The sent recording material S isseparated one by one by the separating means 23 and then is sent towardthe downstream feeding roller pair 10. Thereafter, the recordingmaterial S is fed to the registration roller pair 17 by the feedingroller pair 10 and is once stopped at the registration roller pair 17,and thereafter is sent toward a secondary-transfer portion 15.

On the other hand, in an intermediary transfer belt unit 12 as anintermediary transfer unit, the toner images formed by theprimary-transfer process are carried on the intermediary transfer belt12 e, and then are fed to the secondary-transfer portion 15 by theintermediary transfer belt 12 e. The four color toner images on theintermediary transfer belt 12 e are secondary-transferred, at thesecondary-transfer portion consisting of a secondary-transfer nip, ontothe recording material S fed by the registration roller pair 17 whilebeing timed to the recording material S. That is, at thesecondary-transfer portion 15, a bias is applied to an outersecondary-transfer roller 16, so that the toner images issecondary-transferred from the intermediary transfer belt 12 e onto therecording material S fed to the secondary-transfer portion 15.

At a position opposing a driving roller 12 f as an innersecondary-transfer roller at the surface of the intermediary transferbelt 12 e, the outer secondary-transfer roller 16 is provided. Thisouter secondary-transfer roller 16 is provided in a secondary-transferunit 61 constituted so as to be detachably mountable to the apparatusmain assembly 50 a. The outer secondary-transfer roller 16 sandwichesthe intermediary transfer belt 12 e between itself and the drivingroller 12 f, and the secondary-transfer portion 15 is formed between theouter secondary-transfer roller 16 and the intermediary transfer belt 12e.

The fixing device 14 disposed downstream of the secondary-transferportion 15 includes a fixing belt 14 a in which a heating member 14 c isprovided, and a pressing roller 14 b for forming a fixing nip N betweenitself and the fixing belt 14 a by being pressed against the fixing belt14 a. The fixing belt 14 a consists of an endless cylindrical belt, andis positioned at an outer peripheral surface thereof in a toner imagesurface side on the recording material. The heating member 14 c isdisposed inside the fixing belt 14 a, and the pressing roller 14 b ispress-contacted to the fixing belt 14 a toward the fixing belt 14 a.

In the fixing device 14, when the pressing roller 14 b is rotationallydriven in a driving means (not shown), the fixing belt 14 is rotatedtogether with the pressing roller 146 by the rotation of the pressingroller 14 b, so that the fixing belt 14 a is heated by the heatingmember 14 c. When the recording material S fed from thesecondary-transfer portion 15 is nipped and fed to the fixing nip Nbetween the fixing belt 14 a and the pressing roller 14 b, the tonerimage is heated and pressed at the fixing nip N and then is fixed on therecording material S.

A paper discharging roller pair 20 is provided downstream of the fixingdevice 14. The recording material S subjected to fixing by the fixingdevice 14 is discharged via the paper discharging roller pair 20 onto apaper discharge tray 100 at an upper portion of the apparatus mainassembly 50 a.

Intermediary Transfer Belt Unit

Next, with reference to FIGS. 1 and 2, the intermediary transfer beltunit 12 in this embodiment will be described. Incidentally, FIG. 2 is aperspective view showing a whole of the image forming apparatus 50 sothat a mounting and dismounting direction (arrow R direction) of theintermediary transfer belt unit 12 is understood.

The intermediary transfer belt unit 12 in this embodiment is constitutedas a unit detachably mountable to the apparatus main assembly 50 a. Thisintermediary transfer belt unit 12 is, as shown in FIG. 2, constitutedso that the intermediary transfer belt unit 12 is detachably mountableto the apparatus main assembly 50 a with respect to the arrow Rdirection. At a side portion (right-side portion in FIGS. 1 and 2) ofthe apparatus main assembly 50 a, an openable door 50 b supportedopenably relative to the apparatus main assembly 50 a.

As shown in FIG. 2, when the intermediary transfer belt unit 12 ismounted into and dismounted from the apparatus main assembly 50 a in astate in which the openable door 50 b opens, a guiding portion 62 forguiding the intermediary transfer belt unit 12 in the mounting anddismounting direction (arrow R direction) is provided in both sides ofthe mounting and dismounting direction. In a front side of the guidingportion 62, an inclined guiding surface 62 a for guiding theintermediary transfer belt unit 12 to the guiding portion 62 whilepress-returning the intermediary transfer belt unit 12 against an urgingforce of a driven coupling 47, described later, provided in theintermediary transfer belt unit 12 side is formed. This inclined guidingsurface 62 a is formed also at an unshown guiding portion (62)positioned in the front side in FIG. 2. Further, in a rear side of theguiding portion provided in one side, a driving coupling, describedlater, mounted in the apparatus main assembly side is provided in aprojected state.

The intermediary transfer belt unit 12 includes the intermediarytransfer belt 12 e, a driving roller 12 f as the innersecondary-transfer roller, a follower roller 12 g, the primary-transferrollers 12 a-12 d as the primary-transfer means, and a cleaning device22. Further, the intermediary transfer belt unit 12 includes aprimary-transfer contact-and-separation mechanism 30 (FIG. 3). Theendless belt-like intermediary transfer belt 12 e is stretched by thedriving roller 12 f and the follower roller 12 g, which are a pluralityof rollers, so as to be rotatable in a circumferential direction.

The follower roller 12 g is urged in an arrow E direction in FIG. 1 byan urging means (not shown) thus applying a predetermined tension(force) to the intermediary transfer belt 12 e. The intermediarytransfer belt 12 e is rotated in an arrow F direction in FIG. 1 at apredetermined speed by rotational drive of the driving roller 12 fdriven by a driving force of a motor (not shown).

Each of the primary-transfer rollers 12 a-1 d is provided in an innerperipheral surface side of the intermediary transfer belt 12 e so as tooppose an associated one of the photosensitive drums 1 a-1 d, and isurged toward the associated photosensitive drum by an urging member 31(FIG. 3) such as a compression coil spring. By applying aprimary-transfer bias voltage to each of the primary-transfer rollers 12a-12 d, the toner image formed on the photosensitive drums 1 a-1 d aresuccessively primary-transferred onto the intermediary transfer belt 12e. In this way, when the four color toner images are superposedlyprimary-transferred onto the intermediary transfer belt 12 e, the tonerimages are fed to the secondary-transfer portion 15 by the intermediarytransfer belt 12 e.

When the toner images on the intermediary transfer belt 12 e aresecondary-transferred onto the recording material S at thesecondary-transfer portion 15, the transfer residual toner remaining onthe intermediary transfer belt 12 e is removed by the cleaning device22. Then, the removed transfer residual toner is collected, via atransfer residual toner feeding path (not shown), in a transfer residualtoner collecting container (not shown) provided in the apparatus mainassembly 50 a.

In the intermediary transfer belt unit 12, by the action of theprimary-transfer contact-and-separation mechanism 30, theprimary-transfer rollers 12 a, 12 b, 12 c and Y, M, C controlled to theintermediary transfer belt 12 e toward the photosensitive drums 1 a, 1b, 1 c during the color image formation are separated (spaced) from thephotosensitive drums 1 a-1 d. This operation is performed for extendingthe lifetime of the photosensitive drums 1 a-1 c by avoiding frictionwith the photosensitive drums 1 a-1 c which are not used during imageformation in the operation in the monochromatic mode (Bk single-colormember).

Further, the primary-transfer contact-and-separation mechanism 30 has aseparation constitution of the primary-transfer roller 12 d,corresponding to Bk, operated independently of separation constitutionsof the primary-transfer rollers 12 a, 12 b, 12 c corresponding to Y, M,C. This is because when each of the belt unit 12 and the cartridges 7a-7 d is mounted into and dismounted from the apparatus main assembly 50a for maintenance, damage or the like thereof by friction between theintermediary transfer belt 12 e and the photosensitive drum 1 d isavoided and is prevented from leading to image defect.

Details of Primary-Transfer Contact-and-Separation Mechanism

Next, with reference to FIGS. 3, 4 and 5, details of theprimary-transfer contact-and-separation mechanism 30 will be described.FIG. 3 is a schematic perspective view (including phase G) showing theprimary-transfer contact-and-separation mechanism 30 in this embodiment,FIG. 5 is a schematic perspective view (including phase H) showing theprimary-transfer contact-and-separation mechanism 30, and FIG. 5 is aschematic perspective view (including phase L) showing theprimary-transfer contact-and-separation mechanism 30. In these FIGS.3-5, the intermediary transfer belt 12 e is drawn in a see-throughstate.

The primary-transfer contact-and-separation mechanism 30 includes, asshown in FIGS. 3-5, slidable members 33 a, 33 b, 33 c, 33 d and cammembers 34 a and 34 b ((a) of FIGS. 6) and 34 c and 34 d ((b) of FIG.6). As shown in (a) of FIG. 6, (a) of FIG. 7 and (b) of FIG. 8, the cammembers 34 a and 34 b are fixed at end portions, respectively, of a camshaft 32 so as to have the same phase in a symmetrical shape. As shownin (b) of FIG. 6, (b) of FIG. 7 and (b) of FIG. 8, the cam members 34 cand 34 d are fixed at the end portions, respectively, of the cam shaft32 so as to have the same phase in a symmetrical shape.

The cam shaft 32 is provided and extended in a widthwise direction ofthe intermediary transfer belt unit 12 (the intermediary transfer belt12 e). To this cam shaft 32, a rotational force is transmitted from thedriven coupling 47 via a transmission gear train 49 (FIG. 10).Incidentally, a moving mechanism capable of changing the position of theintermediary transfer belt 12 e to different three positions relative tothe photosensitive drums 1 a-1 d by rotational drive of the drivingmotor 41 is constituted by the cam shaft 32, the cam members (rotatablemembers) 34 a-34 d, the driven coupling 47, the transmission gear train49 and the like.

As shown in FIGS. 3-5, at the end portions of the primary-transferrollers 12 a, 12 b, 12 c, the slidable members 33 a and 33 b areprovided, respectively, and at the end portions of the primary-transferroller 12 d, the slidable member 33 c and 33 d are provided,respectively. The slidable members 33 a and 33 b and the slidablemembers 33 c and 33 d are disposed in parallel with a predeterminedinterval with respect to the widthwise direction of the intermediarytransfer belt 12. Further, each of the slidable members 33 a and 33 band the slidable members 33 c and 33 d is supported by an unshownslidable mechanism so as to be movable in a left-right direction in FIG.3.

The slidable members 33 a and 33 b provided in a pair are moved in anarrow Q direction (circumferential direction of the intermediarytransfer belt 12 e) in FIG. 3 by rotation of the cam members 34 a and 34b provided in a pair. The slidable members 33 c and 33 b provided in apair are moved in the arrow Q direction in FIG. 3 by rotation of the cammembers 34 c and 34 d provided in a pair. Each of the cam members 34 a,34 b, 34 c, 34 d is formed in a sector shape extending around the camshaft 32 having a circular shape in cross-section in a range of 90° withrespect to a radial direction. By the movement of the slidable members33 a-33 d in the arrow Q direction, contact-and-separation positions ofthe primary-transfer rollers 12 a, 12 b, 12 c relative to thephotosensitive drums 1 a, 1 b, 1 c and contact-and-separation positionsof the primary-transfer roller 12 d relative to the photosensitive drumld are changed.

Operations of Slidable Member and Cam Member

Next, operations of the slidable members 33 a-33 d and the cam members34 a-34 d will be specifically described with reference to FIGS. 3-5,(a) and (b) of FIG. 6, (a) and (b) of FIG. 7 and (a) and (b) of FIG. 8.

FIG. 3 corresponds to (a) and (b) of FIG. 6, FIG. 4 corresponds to (a)and (b) of FIG. 7, and FIG. 5 corresponds to (a) and (b) of FIG. 8. InFIG. 6, (a) and (b) are schematic views for illustrating the operationsof the cam members 34 a-34 d and the slidable members 33 a-33 d duringthe color image formation (full-color mode, all contact position). InFIG. 7, (a) and (b) are schematic views for illustrating the operationsof the cam members 34 a-34 d and the slidable members 33 a-33 d duringthe monochromatic image formation (monochromatic mode, partial contactposition). In FIG. 8, (a) and (b) are schematic views for illustratingthe operations of the cam members 34 a-34 d and the slidable members 33a-33 d during all separation (all separation mode, all separationposition).

In the operation in the full-color mode (all contact position), theintermediary transfer belt (member-to-be-moved) 12 e is contacted to allthe photosensitive drums 1 a-1 d which are a plurality of image bearingmembers. In the operation in the monochromatic mode (partial contactposition), the intermediary transfer belt 12 e is contacted to a part(photosensitive drum 1 d) of the photosensitive drums 1 a-1 d. In theoperation in the all separation mode (all separation position), theintermediary transfer belt 12 e is separated from all the photosensitivedrums 1 a-1 d. The controller (control means) 45 switches the full-colormode (all contact position), the monochromatic mode (partial contactposition) and the all separation mode (all separation position) by drivecontrol of the driving motor (driving motor) 41.

Each of the slidable members 33 a and 33 b is provided with an engagingportion 33S₁ having a rectangular space in which an associated one ofthe cam members 34 a and 34 b is insertable. Further, each of theslidable members 33 c and 33 d is provided with an engaging portion 33S₂having a rectangular space in which an associated one of the cam members34 c and 34 d is insertable.

Further, the slidable members 33 a and 33 b are always urged in theright direction in (a) of FIG. 6 by an unshown urging member so as tofollow the rotational operation of the cam members 34 a and 34 binserted in the engaging portion 33S₁. Further, the slidable members 33c and 33 d are always urged in the right direction in (a) of FIG. 6 byan unshown urging member so as to follow the rotational operation of thecam members 34 c and 34 d inserted in the engaging portion 33S₂.

During Full-Color Mode

During the color image formation, by power transmission from a drivetransmitting device 40 described later, to the cam shaft 32, the cammembers 34 a, 34 b in FIG. 3 are in a state of a phase G shown in (a) ofFIG. 6, so that the slidable members 33 a, 33 b are held in a state of aposition J shown in (a) of FIG. 6. As a result, end portions of each ofthe primary-transfer rollers 12 a, 12 b, 12 c with respect to an axialdirection are released from claw portions 38 of each of the slidablemembers 33 a, 33 b, so that the primary-transfer rollers 12 a, 12 b, 12c are pressed by using members 31 and thus are contacted to theintermediary transfer belt 12 e toward the photosensitive drums 1 a, 1b, 1 c, respectively.

At the same time, the cam members 34 c, 34 d in FIG. 3 are in a state ofthe phase G shown in (b) of FIG. 6 by the rotation of the cam shaft 32,so that the slidable members 33 c, 33 d are held in a state of aposition J shown in (b) of FIG. 6. As a result, end portions of theprimary-transfer roller 12 d with respect to the axial direction arereleased from claw portions 39 of the slidable members 33 c, 33 d, sothat the primary-transfer roller Rd is pressed by the urging member 31and thus is contacted to the intermediary transfer belt 12 e toward thephotosensitive drum 1 d.

As described above, during the color image formation, theprimary-transfer rollers 12 a, 12 b, 12 c, 12 d are in an all contactstate in which the primary-transfer rollers 12 a, 12 b, 12 c, 12 d arecontacted to the intermediary transfer belt 12 e toward thephotosensitive drums 1 a, 1 b, 1 c, 1 d, respectively.

During Monochromatic Mode

During the monochromatic image formation, by rotation of the cam shaft32, the cam members 34 a, 34 b in FIG. 4 are rotated by 90° in thecounterclockwise direction (arrow C direction) in (a) of FIG. 7, andthus are in a state of a phase H shown in the figure, so that theslidable members 33 a, 33 b are held in a state of a position K shown inthe figure. That is, the engaging portions 33S₁ of the slidable members33 a and 33 b follow shapes of the cam members 34 a and 34 b, so thateach of the slidable members 33 a and 33 b moves in an arrow D directionby a predetermined distance.

As a result, end portions of each of the primary-transfer rollers 12 a,12 b, 12 c for Y, M, C with respect to the axial direction are raised ina separation direction from the photosensitive drums 1 a, 1 b, 1 c, 1 d,by the claw portions 38 of each of the slidable members 33 a, 33 bagainst the urging force of the urging member 31. For this reason, theprimary-transfer rollers 12 a, 12 b, 12 c are held in the separationstate from the opposing photosensitive drums 1 a, 1 b, 1 c,respectively.

At the same time, the cam members 34 c, 34 d in FIG. 4 are in a state ofthe phase H shown in (b) of FIG. 7 by the rotation of the cam shaft 32,but each of the cam members 34 c, 34 d follow the engaging portion 33S₁at an arcuate end of the sector-shaped portion thereof. For this reason,the slidable members 33 c, 33 d are moved in the arrow D direction andthus are held in the state of the same position J as in (a) of FIG. 6.As a result, the primary-transfer roller 12 d corresponding to Bk ismaintained in the contacted state to the opposing photosensitive drum 1d.

As described above, during the monochromatic image formation, theprimary-transfer rollers 12 a, 12 b, 12 c are retracted from the innerperipheral surface of the intermediary transfer belt 12 e, and thus theintermediary transfer belt 12 e is separated from the photosensitivedrums 1 a, 1 b, 1 c, so that the primary-transfer roller 12 d is in thecontacted state to the associated photosensitive drum 1 d.

During All Separation Mode

During the all separation, by rotation of the cam shaft 32, the cammembers 34 a, 34 b in FIG. 5 and rotated by 90° in the counterclockwisedirection in (a) of FIG. 8, the thus are in a state of a phase L shownin the figure, so that the slidable members 33 a, 33 b are held in astate of the same position K as in (a) of FIG. 7. That is, the engagingportions 33S₁ of the slidable members 33 a and 33 b follow shapes of thecam members 34 a and 34 b, but each of the cam members 34 a and 34 bonly follows the engaging portion 33S₁ at a portion concentrically withthe cam shaft 32.

For this reason, the slidable members 33 c and 33 d are held at the sameposition K as in (a) of FIG. 7 without being moved in the arrow Ddirection. As a result, the primary-transfer rollers 12 a, 12 b, 12 ccorresponding to Y, M, C are held in the separation state from theopposing photosensitive drums 1 a, 1 b, 1 c, similarly as describedabove.

At the same time, the cam members 34 c, 34 d in FIG. 8 are in a state ofthe phase L shown in (b) of FIG. 8 by the rotation of the cam shaft 32,and therefore, each of the cam members 34 c, 34 d is spaced from theengaging portion 33S₁ at the arcuate end of the sector-shaped portionthereof and rotates. As a result, the slidable members 33 c, 33 d aremoved in the arrow D direction and thus are in the position K. For thisreason, the primary-transfer roller 12 d is held in the separated statefrom the opposing photosensitive drum 1 d.

As described above, during the all separation, all the primary-transferrollers 12 a, 12 b, 12 c, 12 d are retracted from the inner peripheralsurface of the intermediary transfer belt 12 e, and thus theintermediary transfer belt 12 e is separated from the photosensitivedrums 1 a, 1 b, 1 c, 1 d, so that the primary-transfer rollers 12 a-12 dare in the all separation state in which the intermediary transfer belt12 e is separated from the photosensitive drums 1 a-1 d.

Drive Transmitting Device Including Driving Coupling

Next, with reference to FIG. 9, the drive transmitting device 40 in thisembodiment will be specifically described. FIG. 9 is a schematicperspective view showing the drive transmitting device 40 in thisembodiment.

As shown in FIG. 9, the drive transmitting device 40 includes thecontroller 45 as the control means and the driving motor 41 consistingof the pulse motor (stepping motor) or the like driven by control by thecontroller 45. Further, the drive transmitting device 40 includes apinion 41 b fixed to a rotation shaft 41 a of the driving motor 41. Inaddition, the drive transmitting device 40 includes a transmitting gear42 engaging with the pinion 41 b, a flag gear 43 engaging with thetransmitting gear 42, and a sensor 44 for detecting a flag portion(light-blocking portion) 43 a. Further, the pinion 41 b, thetransmitting gear 42 and the flag gear 43 are supported so that therotation shaft 41 a, a rotation shaft 42 c and a rotation shaft 43 c areparallel to each other with respect to their axis directions.

Incidentally, the flag portion 43 a constitutes a flag showing apredetermined rotational position of the driving motor (pulse motor) 41,and the sensor 44 constitutes a detecting portion for detecting the flagportion 43 a. The flag portion (flag) 43 a is rotated in synchronismwith the position of the intermediary transfer belt (member-to-be-moved)12 e, and thus is disposed at a position corresponding to a specificrotation phase range of each of the cam members (rotatable members) 34a-34 d provided in the moving mechanism (32, 34 a-34 d, 47, 49).

Further, the controller 45 controls the moving mechanism (32, 34 a-34 d,47, 49) using either one of an operation in a first stop mode anoperation in a second stop mode. The first stop mode is a mode in whichthe moving mechanism is stopped on the basis of detection (result) ofthe sensor (detecting portion) 44 when the intermediary transfer belt(member-to-be-moved) 12 e is changed in position (arrangement) of thedifferent three positions (arrangements), from one position(arrangement) to another position (arrangement). The second stop mode isa mode in which the moving mechanism is stopped on the basis of thenumber of pulses of a driving signal sent to the driving motor (pulsemotor) 41.

The controller 45 uses the first stop mode when the intermediarytransfer belt (member-to-be-moved) 12 e is changed in position of thethree positions from the second position or the third position to thefirst position. Further, the controller 45 uses the second stop modewhen the intermediary transfer belt position is changed from the firstposition or the third position to the second position or when theintermediary transfer belt position is charged from the first positionor the second position to the third position. The controller 45 controlsthe moving mechanism (32, 34 a-34 d, 47, 49) s that at least the changein position between the second position and the third position is madeonly by unidirectional rotational drive of the driving motor 41.

Further, the driving coupling 46 is disposed in the apparatus mainassembly 50 a side. In the intermediary transfer belt unit 12, at aposition capable of opposing the driving coupling 46 during the mountingand dismounting, the driven coupling 47 (FIG. 10) is disposed. Thedriving coupling 46 is mounted on the rotation shaft 43 c of the flaggear 43 so as to be positioned in a side opposite from the gear portion43 b with respect to the axial direction.

The transmitting gear 42 is coaxially provided with a large-diametergear 42 a engaging with the pinion 41 b and a small-diameter gear 42 bsmaller in diameter than the large-diameter gear 42 b. The flag gear 43includes a large-diameter gear 43 b engaging with the small-diametergear 42 b and the flag portion (light-blocking portion) 43 a projectingfrom the gear portion 43 b in the axial direction so as to extend in anarcuate shape in cross-section. The rotational force of the drivingmotor 41 is transmitted to the large-diameter gear 42 a via the pinion41 b, so that the transmitting gear 42 is rotated. The rotational forceis also transmitted to the gear portion 43 b via the small-diameter gear42 b, s that the driving coupling 46 is rotated together with the flaggear 43 in the same direction.

The sensor 44 is a sensor of a photo-interrupter type in which alight-emitting portion 44 a and a light-receiving portion 44 b areprovided and in which a detection signal is outputted by switchinglight, between a light-blocking state and a light-transmissionsecondary-transfer, blocked in or passed through a gap (spacing) 44 c,between the light-emitting portion 44 a and the light-receiving portion44 b, in which the flag portion 43 a moves. When the flag portion 43 aenters the gap 44 c, the sensor 44 detects the flag portion 43 a andthen sends a flag ON signal to the controller 45, and when the flagportion 43 a does not enter the gap 44 c, the sensor 44 does not detectthe flag portion 43 a.

Transmitting Gear Train Including Driven Coupling

In the intermediary transfer belt unit 12 side, as shown in FIG. 10, thedriven coupling 47, an urging member 48, and a transmitting gear train49 for transmitting the rotational force, to the cam shaft 32,transmitted from the driving coupling 46 to the driven coupling 47. Thistransmitting gear train 49 is constituted by gears 49 a, 49 b, 49 c, 49d. The driven coupling 47 connectable to the driving coupling 46transmits the rotational force thereof to a gear 58 fixed coaxially withthe driven coupling 47, and the rotational force of this gear 58 istransmitted, via the transmitting gear train 49, to the cam shaft 32connected to the gear 49 d.

The gear 58 is urged in an arrow B direction, i.e., toward the apparatusmain assembly 50 a, by the urging member 48 consisting of a compressioncoil spring. The driven coupling 47 is disposed so as to oppose thedriving coupling 46 in a state in which the intermediary transfer beltunit 12 is mounted in the apparatus main assembly 50 a.

The driven coupling 47 is pressed into an arrow M direction against theurging member 48 by a pressing force when the intermediary transfer beltunit 2 is guided from the inclined guiding surface 62 a to the guidingportion 62 during the mounting of the intermediary transfer belt unit 12into the apparatus main assembly 50 a (FIG. 2). Then, when theintermediary transfer belt unit 12 is properly mounted, at this time,the driven coupling 47 is released from the guiding portion 62 and isprojected by the urging force of the urging member 48, thus engagingwith the driving coupling 46. As a result, the driven coupling 47 isrotated by the transmission of the rotational force of the driving motor41 via the driving coupling 46.

Positional Relationship Between Flag Portion and Sensor

A positional relationship between the flag portion 43 a and the sensor44 will be described with reference to FIGS. 9, 15 and 17. FIG. 15 is aschematic view showing operations each between the flag portion 43 a andthe sensor 44 of the drive transmitting device 40 in this embodiment,and shows a state as seen from an arrow U direction in FIG. 9. FIG. 17is a schematic view showing a rotational position of the flag gear 43 inthis embodiment, and shows a state as seen from the arrow U direction inFIG. 9.

In FIG. 15, an indicated symbol “A” represents a positional relationshipbetween the flag portion 43 a and the sensor 44 during the operation inthe full-color mode (color image formation). This state “A” correspondsto the phase G (FIG. 3 and (a) and (b) of FIG. 6) of the cam members 34a-34 d in the primary-transfer contact-and-separation mechanism 30. Atthis time, in the intermediary transfer belt unit 12, as shown in FIGS.3 and 6, each of the cam members 34 a, 34 b and the cam members 34 c, 34d is in the phase G, and therefore each of the slidable members 33 a, 33b and the slidable members 33 c, 33 d is held at the position J.

In FIG. 17, the flag portion 43 a of the flag gear 43 is in the phase Gindicated by a solid line, and a width (arcuate length) with respect toa circumferential direction is W. In the case where the arcuate lengthof the flag portion 43 a is W, when the flag portion 43 a is rotated inthe counterclockwise direction (CCW direction) in FIG. 17 by the driveof the driving motor 41, a time required to rotate the flag portion 43 afrom the phase G to the phase H is T1. Further, when the flag portion 43a is rotated in the clockwise direction (CW direction) in FIG. 17 by thedrive of the driving motor 41, a time required to rotate the flagportion 43 a from the phase H to the phase G is T2. Further, when theflag portion 43 a is rotated in the counterclockwise direction (CCWdirection) in FIG. 17 by the drive of the driving motor 41, a timerequired to rotate the flag portion 43 a from the phase H to the phase Lis T3.

From the above state “A”, when the flag gear 43 is rotated in thecounterclockwise direction (CCW direction) by further rotation of thedriving motor 41, the state is changed to a state indicated by a symbol“B” in FIG. 15. This state “B” corresponds to the phase H (FIG. 4 and(a) and (b) of FIG. 7) of the cam members 34 a-34 d in theprimary-transfer contact-and-separation mechanism 30. In FIG. 17, theflag portion 43 a moves to the phase H indicated by a broken line byadvance of the time T1 with respect to a center of the arcuate length W.

In this case, in the intermediary transfer belt unit 12, as shown inFIGS. 4 and 7, the cam members 34 a, 34 b and the cam members 34 c, 34 dis in the phase H. However, as described above, the slidable members 33a, 33 b move to the position K, but the slidable members 33 c, 33 dremain at the position J. As a result, the intermediary transfer beltunit 12 is in the state of the monochromatic mode (Bk single-colormode).

From the above state “B”, when the flag gear 43 is rotated in thecounterclockwise direction (CCW direction) by further rotation of thedriving motor 41, the state is changed to a state indicated by a symbol“C” in FIG. 15. This state “C” corresponds to the phase L (FIG. 5 and(a) and (b) of FIG. 7) of the cam members 34 a-34 d in theprimary-transfer contact-and-separation mechanism 30. In FIG. 17, theflag portion 43 a moves to the phase L indicated by a broken line byadvance of the time T3 from the phase H with respect to a center of thearcuate length W.

In this case, in the intermediary transfer belt unit 12, as shown inFIGS. 5 and 8, the cam members 34 a, 34 b and the cam members 34 c, 34 dis in the phase L, and as described above, the slidable members 33 a, 33b remain at the position K, but the slidable members 33 c, 33 d move tothe position J. As a result, the intermediary transfer belt unit 12 isin the state of the all separation mode.

Next, a switching operation from the full-color mode to themonochromatic mode will be described with reference to FIGS. 15, 17 and18. FIG. 18 is a flowchart showing a contact flow of switching from thefull-color mode to the monochromatic mode.

First, the driving motor 41 responsive to the control by the controller45 drives the flag portion 43 a so as to rotate in the counterclockwisedirection (CCW direction) in FIG. 17 (step S1). On the basis of outputof a flag OFF signal by movement of the flag portion 43 a into the gap44 c, when the controller 45 detects the flag OFF signal (S2: Yes), thecontroller 45 awaits a lapse of a time of (T1−W/2) (S3: Yes), and thenstops the driving motor 41 (S4).

Then, the controller 45 discriminates, on the basis of the detection ofthe sensor 44, whether or not the flag OFF signal is outputted (S5), andwhen the flag OFF signal is outputted (S5: Yes), ends a process, andwhen the flag OFF signal is not outputted (S5: No), discriminates thatan error occurs (S6). During the occurrence of the error, e.g., at anoperating portion (not shown) provided on the apparatus main assembly 50a, a massage such as “PLEASE CONTACT SERVICE PERSON” is displayedtogether with an arrow code (number in a plurality digits), so that itis possible to stop the operation of the apparatus main assembly 50 a.

Next, a switching operation from the monochromatic mode to thefull-color mode will be described with reference to FIGS. 15, 17 and 19.FIG. 19 is a flowchart showing a contact flow of switching from themonochromatic mode to the full-color mode.

First, the driving motor 41 responsive to the control by the controller45 drives the flag portion 43 a so as to rotate in the counterclockwisedirection (CW direction) in FIG. 17 (S11). Then, the controller 45awaits a lapse of a time of T2 (S12: Yes), and then stops the drivingmotor 41 (S13) and then the flag portion 43 a enters the gap 44 c, andthe controller 45 checks the flag ON signal (S14).

Then, the controller 45 ends a process when checked the flag OFF signal(S14: Yes), and discriminates that an error occurs (S15) when checked noflag OFF signal (S14: No).

Next, a switching operation from the full-color mode to the allseparation mode will be described with reference to FIGS. 15, 17 and 20.FIG. 20 is a flowchart showing a contact flow of switching from thefull-color mode to the all separation mode.

First, The driving motor 41 drives the flag portion 43 a so as to rotatein the counterclockwise direction (CCW direction) in FIG. 17 in responseto the control by the controller 45 (step S21). Next, when thecontroller 45 detects the flag OFF signal (S22: Yes), the controller 45awaits a lapse of a time of (T1+T3−W/2) (S23: Yes), and then stops thedriving motor 41 (S24) and checks the flag OFF signal (S25). Then, thecontroller 45 ends a process when checked the flag OFF signal (S25: Yes)and discriminates that an error occurs (S26) when checked no flag OFFsignal (S25: No).

As described above, the controller in this embodiment controls the threepositions of the intermediary transfer belt 12 e as themember-to-be-moved to be moved via the primary-transfer rollers 12 a-12d in the following manner. That is, the different three positions(arrangements) are the all contact position (arrangement), the partialcontact position (arrangement) and the all separation position(arrangement). As described above, the all contact position is aposition where all the photosensitive drums 1 a-1 d and the intermediarytransfer belt 12 e contact each other. The partial contact position is aposition where a part (1 d) of the photosensitive drums 1 a-1 d and theintermediary transfer belt 12 e contact each other. The all separationposition is a position where all the photosensitive drums 1 a-1 d andthe intermediary transfer belt 12 are separated from each other.

The controller 45 effects the following control when the first position(e.g., the all contact position (full-color mode) is based on detectionof the flag portion 43 a by the sensor 44, and the second and thirdpositions are based on the pulse number of the driving signal withoutdetecting the flag portion 43 a by the sensor 44. That is, thecontroller 45 controls the moving mechanism so that a change in positionat least between the second position (e.g., the partial contact position(monochromatic mode)), and the third position (e.g., the all separationposition (all separation mode)) only be unidirectional rotational drive(FIG. 15).

In other words, the above three positions are the first position (e.g.,the state “A” in FIG. 15), the second position (e.g., the state “B” inFIG. 15), and the third position (e.g., the state “C” in FIG. 15). Thefirst position is the position on the basis of the detection of the flagportion 43 a by the sensor 44, and the second position and the thirdposition are the positions on the basis of the pulse number of thedriving signal sent to the driving motor 41 without detecting the flagportion 43 a by the sensor 44. In this case, the controller 45 effectscontrol so that the movement at least between the second position andthe third position is made only by unidirectional rotation of thedriving motor 41. As a result, prolongation of a mode switching time anda device rise time is avoided and at the same time, productivity isenhanced by suppressing prolongation of downtime, so that it becomespossible to prevent an occurrence of problems such as a user stress,shortening of lifetime of the apparatus.

The controller 45 makes the change in position of the intermediarytransfer belt 12 e between the first position (e.g., the state “A”) andthe second position (e.g., the state “B”) by bi-directional rotation ofthe driving motor 41. Further, the controller 45 effects control so thatthe change in position between the first position and the third position(e.g., the state “C”) by the unidirectional rotation of the drivingmotor 41. As a result, the state transfer in the order of the state “A”,the state “B” and the state “C” can be made only by the unidirectionalrotation (in the counterclockwise direction) of the driving motor 41,and therefore it is possible to contribute to backlash elimination suchthat so-called backlash of the gears or the like from the driving motor41 to the cam shaft 32 is eliminated.

Alternatively, the control by the controller 45 is partly changed,whereby it is also possible to carry out the control as shown in FIG.16. That is, the control is effected so that the change in position ofthe intermediary transfer belt 12 e between the first position and thesecond position is made by the bi-directional rotation of the drivingmotor 41 and also the change between the first position and the thirdposition is made by the bi-directional rotation of the driving motor 41.In this case, an effect with respect to the backlash elimination asdescribed above is somewhat decreased, but the effects such that theprolongation of the mode switching time and the apparatus rise time andthe enhancement in productivity by the suppression of the downtimeprolongation can be similarly obtained.

Drive-Connecting Mechanism During Mounting and Dismounting ofIntermediary Transfer Belt Unit

Next, with reference to FIGS. 11-14, the coupling portion used when theintermediary transfer belt unit 12 is mounted into and dismounted fromthe apparatus main assembly 50 a will be described. In FIG. 11, (a) to(d) are schematic views showing the coupling portion.

The intermediary transfer belt 12 e is constituted so as to be mountableinto and dismountable from the apparatus main assembly 50 a at the allseparation position during the operation in the all separation mode bythe mounting and dismounting of the intermediary transfer belt 12relative to the apparatus main assembly 50 a. In this apparatus mainassembly side, the above-described driving motor (pulse motor) 41 isprovided. Further, the coupling portion which is provided connectablyand separably between the driving motor 41 and the intermediary transferbelt 12 e and which is capable of transmitting power between the drivingmotor 41 and the intermediary transfer belt 12 e in a connected state isprovided.

That is, the intermediary transfer belt unit 12 includes theintermediary transfer belt 12 e and the moving mechanism (32, 34 a-34 d,47, 49) and is disposed so as to be mountable in and dismountable fromthe apparatus main assembly 50 a. The coupling portion is providedbetween the driving motor 41 provided in the apparatus main assembly 50a side and the moving mechanism, and when the position of theintermediary transfer belt 12 e relative to the photosensitive drums 1a-1 d is the all detection position, enables switching betweentransmission and elimination of power between the driving motor 41 andthe moving mechanism.

This coupling portion includes, as shown in FIG. 10 and FIGS. 11-14, thedriving coupling 46 and the driven coupling 47 which are connectable andseparable at the all separation position. As a result, only by movingthe intermediary transfer belt unit 12 in an inserting and pulling-outdirection along the guiding portion 62 (FIG. 2) provided in theapparatus main assembly 50 a side, this belt unit 12 can be dismountedfrom and mounted in the apparatus main assembly 50 a very simply andwith reliability.

That is, the driving coupling 46 and the driven coupling 47 are, asshown in (a) of FIG. 11, constituted as cylindrical members such thatthe driving coupling 46 is somewhat larger in diameter than the drivencoupling 47 so that the couplings are engageable with each other in anopposed state.

In an engaged state between the driving coupling 46 and the drivencoupling 47 shown in FIG. 10, a second engaging portion 47 a of thedriven coupling 47 shown in FIG. 11 contacts an inclined surface 46 e((c) of FIG. 11) provided at an inner periphery of the driving coupling46. For that reason, when the intermediary transfer belt unit 12 ispulled out from the apparatus main assembly 50 a, a pulling-out forceacts on the intermediary transfer belt unit 12 in the mounting anddismounting direction (the arrow A direction in FIG. 12, the arrow Rdirection in FIG. 2), so that the second engaging portion 47 a slides onthe inclined surface 46 e.

As a result, a force for moving the driven coupling 47 in an arrow Mdirection opposite to an urging direction (the arrow B direction in FIG.10) by an urging member 48 acts on the driven coupling 47. For thisreason, the driven coupling 47 temporarily retracts from the drivingcoupling 46 in the arrow M direction, and when engagement between thefirst engaging portion 46 b and the second engaging portion 47 a iseliminated, it is possible to pull out the intermediary transfer beltunit 12 from the apparatus main assembly 50 a.

As shown in (c) of FIG. 11, in the inner periphery side of the inclinedsurface 46 e in the driving coupling 46, the first engaging portion 46 bis formed so as to project in “T-shape” from a bottom 46 a formed in aflat shape. On the other hand, as shown in (b) of FIG. 11, in a sidewhere the driven coupling 47 opposes the driving coupling 46, the secondengaging portion 47 a engageable so as to sandwich the T-shaped firstengaging portion 46 b from above, below, left and right is formed so asto project from an edge portion of a flat surface 47 b. Further, asshown in (d) of FIG. 11, when the driving coupling 46 is rotated in,e.g., an arrow L direction, the contact surface 46 c of the T-shapedfirst engaging portion 46 b rotates the driven coupling 47 in the samedirection via the second engaging portion 47 a while engaging with thesecond engaging portion 47 a.

The coupling portion will be described below further specifically withreference to FIGS. 12 and 13. In FIG. 12, (a) to (c) are schematic viewsshowing a state of the coupling portion before disengagement of theintermediary transfer belt unit 12 starts. In FIG. 13, (a) to (c) areschematic views showing a state in which the contact between the firstand second engaging portions of the coupling portion is eliminated. InFIG. 14, (a) to (c) are schematic views showing a distance betweenrotation shafts of the coupling portion.

In each of FIGS. 12 and 13, (a) shows a state of engagement between thedriving coupling 46 and the driven coupling 47. Further, (b) of FIG. 12and (b) of FIG. 13 are sectional views each showing the engagement statebetween the driving coupling 46 and the driven coupling 47 as seen froma direction perpendicular to the rotation shaft. Further, (c) of FIG. 12and (c) of FIG. 13 are schematic views each showing the engagement statebetween the driving coupling 46 and the driven coupling 47 as seen froma rotational axis direction.

In a state before the intermediary transfer belt unit 12 is disengagedfrom the apparatus main assembly 50 a, the engagement state is as shownin (b) of FIG. 12. That is, of the three second engaging portions 47 a,between the second engaging portion positioned in an upstreammost sidewith respect to an intermediary transfer belt unit disengagementdirection (hereinafter this second engaging portion is referred to as asecond engaging portion 47 f) and the contact surface 46 c of the firstengaging portion 46 b, a sufficient gap is created with respect to therotational direction. This is because at this time, the flag gear 43 isin the state of the phase L (FIGS. 5 and 8), and as described above, thetransfer to the phase L is always made only by the rotation from thephase H in the CCW direction (FIGS. 15 and 16).

When the intermediary transfer belt unit 12 is pulled out from theapparatus main assembly 50 a in a direction perpendicular to therotation shaft J of the driving coupling 46, by a force acting in thisdisengagement direction of the unit 12, the driven coupling 47rotationally moves so that the second engaging portion 47 f approachesthe contact surface 46 c. At this time, the driven coupling 47 is in aposition, as a center of the rotational movement, which is differentfrom the rotation shaft J of the driving coupling 46 and where thedriving coupling 46 and the driven coupling 47 contact each other.

As shown in (c) of FIG. 12 and (c) of FIG. 13, the second engagingportion positioned between the second engaging portion 47 f and thefirst engaging portion 46 b is hereinafter referred to as a secondengaging portion 47 h. Accordingly, a position k where the secondengaging portion 47 h and the contact 46 c contact each other is thecenter of rotational movement.

When the driven coupling 47 starts the rotational movement at theposition k as the center, the second engaging portion 47 f approachestoward the contact surface 46 c of the first engaging portion 46 b, andtherefore the gap between the second engaging portion 47 f and thecontact surface 46 c is decreased. When the driven coupling 47 isrotationally moved, the second engaging portion positioned in adownstreammost side of the second engaging portions 47 a with respect tothe disengagement direction of the intermediary transfer belt unit 12(hereinafter, this second engaging portion is referred to as a secondengaging portion 47 g) moves to the disengagement direction (the arrow Mdirection) of the belt unit 12 along the inclined surface 46 e.

As a result, the driven coupling 47 retracts in the disengagementdirection (the arrow M direction), and therefore as shown in (a) to (c)of FIG. 13, the engagement between the first engaging portion 46 b andeach of the second engaging portions 47 f, 47 g and 47 h is eliminated.That is, from the contact surface 46 c of the first engaging portion 46b, the contact surface of each of the second engaging portions 47 f, 47g and 47 h is separated (spaced). Until the engagement between the firstengaging portion 46 b and each of the second engaging portions 47 f, 47f and 47 h is eliminated, a distance in which a rotation shaft V of thedriven coupling 47 moves in the unit disengagement direction relative tothe rotation shaft J of the driving coupling 46 is β.

Next, when the belt unit 12 is pulled out in the direction perpendicularto the rotation shaft J of the driving coupling 46, a structure in whichthe rotation shaft V of the driven coupling 47 is movable in thedisengagement direction relative to the rotation shaft J by the forceacting in the disengagement direction will be described.

That is, as is understood from (a) to (d) of FIG. 11, the drivencoupling 47 has a region which is sufficiently broad for engagement ofthe driving coupling 46 therein. As a result, a clearance is formed whenthe driving coupling 46 and the driven coupling 47 rotate in theengagement state.

As shown in (a) to (d) of FIG. 14, a maximum distance in which therotation shaft J of the driven coupling 47 is movable in the unitdisengagement direction (the arrow A direction) relative to the rotationshaft J of the driving coupling 46 is α.

The coupling portions (46, 47) in this embodiment are constituted sothat the distance α is larger than the distance β. The distance α is notless than the distance β, whereby when the driven coupling 47 rotates atthe position k as the center, the retraction of the driven coupling 47in the arrow M direction is completed before the second engaging portion47 f contacts the first engaging portion 46 b.

Accordingly, according to the constitution using the coupling portion inthis embodiment, only by pulling out the belt unit 12 from the apparatusmain assembly 50 a, the engagement of the first engaging portion 46 bwith each of the second engaging portions 47 f, 47 g and 47 h can beeliminated simply with reliability. As a result, the engagement betweenthe driving coupling 46 and the driven coupling 47 can be eliminatedsimply. On the other hand, only by inserting the belt unit 12 into theapparatus main assembly 50 a along the guiding portion 62 of theapparatus main assembly 50 a, the belt unit 12 can be mounted in theapparatus main assembly 50 a very simply with reliability.

In this embodiment, as described with reference to FIG. 15, in a seriesof mode switching operations, the flag gear 43 is rotated only in theCCW direction by the power of the driving motor 41, but only when theoperation is switched from the operation in the monochromatic mode tothe operation in the full-color mode, the driving motor 41 is rotated inthe CW direction. Further, the position of the sensor 44 is disposed atthe phase G for the full-color mode.

The reason thereof is that a sufficient gap with respect to therotational direction is created between the second engaging portion 47 aand the contact surface 46 c of the first engaging portion 46 to enablesimple disengagement of the intermediary transfer belt unit 12 from theapparatus main assembly 50 a. In the switching, high in switchingfrequency, between the monochromatic mode and the full-color mode, whenshortest switching is intended to be made by repetitively switching themotor rotational direction without disposing the sensor 44 at the phasefor the full-color mode, there is a possibility that a deviation in stopphase of the flag portion 43 a is accumulated. Also this problem isintended to be avoided.

An effect obtained by employing the constitution in this embodiment willbe described while making reference to Comparison Example shown in (a)and (b) of FIG. 21.

In this Comparison Example, a constitution in which the sensor 44detects the flag ON state by using a flag gear 43′ when the flag ispositioned at the position for the all separation mode as shown in (a)and (b) of FIG. 21 is employed. In this constitution, when the switchingbetween the full-color mode and the monochromatic mode is made byrepetitively switching the motor rotational direction, the deviation instop position of the flag portion 43 a is accumulated.

For example, in the case where the phase is switched from the phase Gfor the full-color mode to the phase H for the monochromatic mode, whenthe stop position of the flag portion 43 a is deviated by disturbance asshown in (a) of FIG. 21, the operation starts from a phase H′, not thephase H when the position is subsequently returned from the phase H tothe phase G. For this reason, when the disturbance further occurs whenthe flag portion 43 a stops at the phase G, there is a liability thatthe deviation is accelerated.

In this way, when the deviation in stop position is accumulated, theprimary-transfer rollers compatible with the colors are rotated althoughthe monochromatic mode is intended, so that there is a liability thatproblems that a lowering in lifetime of the apparatus is caused and thatwhite paper is outputted by start of the image forming operation in thestate in which all the primary-transfer rollers are separated occur.

On the other hand, according to the constitution in this embodiment, theswitching is made in a shorter (shortest) time, and therefore even whenthe rotational direction of the driving motor 41 is repetitivelyswitched, flag ON detection by the sensor 44 is made once per twoswitching operations, and therefore the image forming apparatus 50 canbe operated with no accumulation of the error. As a result, it becomespossible to improve productivity without impairing the lifetime of theimage forming apparatus 50.

Further, as another Comparison Example, it would be also considered thatin order to prevent the error accumulation, flags different in widthfrom each other are disposed at all of the phase positions of the flaggear. However, in this case, there is a need to always rotate the motorfor distinguish the mode in order to detect the flag ON state in all ofthe modes, so that a problem such that the downtime is prolonged duringpower-on of the apparatus main assembly 50 a and during reset of theapparatus main assembly 50 a generates.

According to the constitution in this embodiment, the flag ON state isdetected only at a home position (full-color mode), and therefore duringthe power-on of the apparatus main assembly 50 a and during the reset ofthe apparatus main assembly 50 a, the driving motor 41 may only berequired to be rotated only in the case where the flag ON state is notdetected, and therefore it is possible to alleviate the prolongation ofthe downtime.

Second Embodiment

Second Embodiment in which the present invention is applied to thesecondary-transfer unit 61 of the image forming apparatus 50 will bedescribed with reference to FIGS. 22 and 23. In FIG. 22, (a) is asectional view showing a state in which the outer state roller in thisembodiment is contacted to the intermediary transfer belt toward thedriving roller, and (b) is sectional view showing a state in which theouter secondary-transfer roller is moved to stand-by position. FIG. 23is a sectional view showing a state in which the outersecondary-transfer roller is moved to a separation position. In thisembodiment, the same members or portions as those in First Embodimentare represented by the same reference numerals or symbols, and themembers or portions having the same structures and functions as those inFirst Embodiment will be omitted from description thereof.

As shown in (a) and (b) of FIG. 22, the secondary-transfer unit 61detachably mountable to the apparatus main assembly 50 a (FIG. 1)includes the outer secondary-transfer roller (transfer roller) 16, aroller contact-and-separation mechanism 63 for moving the outersecondary-transfer roller 16, and a contact-and-separation driving unit68. The roller contact-and-separation mechanism 63 includes a supportingmember 69 supported by the apparatus main assembly 50 a of the imageforming apparatus 50 so as to be disposed at a position opposing thedriving roller (the inner secondary-transfer roller) 12 f. Thesupporting member 69 is provided with a secondary-transfer arm 53 havinga shape such that the secondary-transfer arm 53 is somewhat bent so asto be positioned at a central portion. At the central portion of thesecondary-transfer arm 53, a rotational movement supporting hole 53 a isformed.

On the supporting member 69, an accommodating portion 64 formed in asubstantially rectilinear shape toward the driving roller 12 f isformed. In the accommodating portion 64, a roller holder 70 isaccommodated in a state in which the roller holder 70 is movable towardthe driving roller 12 f and is prevented from projecting toward thedriving roller 12 f more than the position shown in (a) of FIG. 22. Inthe accommodating portion 64, in a side of the roller holder 70 oppositefrom the driving roller 12 f, a holder urging spring 52 consisting of acompression spring is provided in a compressed state between a rear endportion of the roller holder 70 and a bottom 64 a.

The roller holder 70 is provided with a projected portion 67 projectingtoward the front side in (a) and (b) of FIG. 22. This projected portion67 is slidably inserted into the rotational movement supporting hole 53a of the secondary-transfer arm 53. The secondary-transfer arm 53 issupported, at a base end portion thereof, rotatably relative to thesupporting member 69 by a rotational movement supporting shaft 66, andat a free end portion thereof, a rotatable circular plate-shapedmember-to-be-urged 65 is supported.

By the above constitution, the outer secondary-transfer roller 16 iscontacted (press-contacted) to the driving roller 12 f by an urgingforce of the holder urging spring 52 in a state in which an rotationshaft 51 is held by the roller holder 70. The roller holder 70 and theouter secondary-transfer roller 16 are constituted so as to movable in acontact direction toward the driving roller 12 f and a separationdirection from the driving roller 12 f by the secondary-transfer arm 53held rotatably about the rotation movement supporting shaft 66 as thecenter. When the outer secondary-transfer roller 16 is moved in thecontact direction, the outer secondary-transfer roller 16 ispress-contacted to the driving roller 12 f in the form such that theintermediary transfer belt 12 e is sandwiched between itself and thedriving roller 12 f.

At a position where the supporting member 69 opposes themember-to-be-urged 65, a cam supporting shaft 55 for supporting aneccentric cam 54 is provided. The member-to-be-urged 65 is contacted tothe eccentric cam 54, supported by the cam supporting shaft 55 in astate in which a center position is deviated, via the secondary-transferarm 53 urged at the central portion by the holder urging spring 52.

In this embodiment, onto the intermediary transfer belt 12 e as theimage bearing member, the toner images carried on the photosensitivedrums 1 a-1 d as other image bearing members are transferred. Further,the outer secondary-transfer roller (transfer roller) 16 as themember-to-be-moved form the secondary-transfer portion (nip) 15 betweenitself and the intermediary transfer belt 12 e, and the toner images aretransferred from the intermediary transfer belt 12 e onto the recordingmaterial S passing through the secondary-transfer portion 15.

Then, the cam supporting shaft 55 is rotated by drive of a motor 71consisting of the pulse motor provided in the contact-and-separationdriving unit 68 in a state in which the cam supporting shaft 55 fixesand supports the eccentric cam 54 and is supported rotatably relative tothe supporting member 69, thus rotating the eccentric cam 54. Theeccentric cam 54 is rotated by the drive of the motor 71 driven bycontrol by the controller 45 (FIG. 1) to change a contact position(contact phase) with the member-to-be-urged 65, whereby the outersecondary-transfer roller 16 is moved along a contact position, astand-by position (intermediary position) and a separation position.

That is, different three positions of the outer secondary-transferroller 16 relative to the intermediary transfer belt 12 e are thecontact position, the separation position and the stand-by position(intermediary position). The contact position is a position where theouter secondary-transfer roller 16 and the intermediary transfer belt 12e contact each other. The separation position is a position where thesecondary-transfer unit (transfer unit) 61 including the outersecondary-transfer roller 16 is detachably mountable to the apparatusmain assembly 50 a (FIG. 1) and where the outer secondary-transferroller 16 and the intermediary transfer belt 12 e are separated fromeach other. The stand-by position (intermediary position) is a positionbetween the separation position and the contact position.

In this way, the controller 45 as the control means effects control sothat the position of the outer secondary-transfer roller 16 is switchedamong the contact position, the stand-by position and the separationposition by drive control of the motor (pulse motor) 71. In other words,the contact position is a position when the secondary-transfer iscarried out during printing, and the stand-by position is a positionwhere the outer secondary-transfer roller 16 is separated when thereference toner pattern (correction patch) is formed on the intermediarytransfer belt during the printing. Further, the separation position is aseparation position in a period other than during the printing. At thestand-by position, a necessary minimum separation amount in which thecorrection patch is not deposited on the outer secondary-transfer roller16 in the case where the correction patch passes through the nip isensured. At the separation position, a separation amount inconsideration of a jam paper clearance property or an insertion andpulling-out property of the secondary-transfer unit 61 relative to theapparatus main assembly 50 a during maintenance or transportation isensured. In the present invention, the first position corresponds to the“contact position”, the second position corresponds to the “stand-byposition (intermediary position)”, and the third position corresponds tothe “separation position”.

In this embodiment, the contact position, the stand-by position and theseparation position correspond to the phase G, the phase H and the phaseL (FIGS. 15 and 16), respectively, in First Embodiment. Also in such anembodiment, an effect substantially similar to the effect in FirstEmbodiment can be obtained.

While the invention has been described with reference to the structuresdisclosed herein, it is not confined to the details set forth and thisapplication is intended to cover such modifications or changes as maycome within the purpose of the improvements or the scope of thefollowing claims.

This application claims priority from Japanese Patent Application No.212983/2013 filed Oct. 10, 2013, which is hereby incorporated byreference.

1-8. (canceled)
 9. An image forming apparatus comprising: an imagebearing member; a motor rotatable bi-directionally; a moving mechanism,including a cam rotated by said motor, capable of changing a position ofa member-to-be-moved to three different positions relative to said imagebearing member by switching a phase of said cam; a sensor configured todetect the phase of said cam; and a controller configured to controldrive of said motor on the basis of a detection result of said sensor,wherein the three positions are a first position where themember-to-be-moved is disposed during image formation, a second positionwhere the member-to-be-moved is disposed during the image formation andwhich is different from the first position, and a third position wherethe member-to-be-moved is not disposed during the image formation,wherein said sensor is capable of detecting the phase of said camcorresponding to the first position, and wherein said moving mechanismis configured to move the member-to-be-moved so that themember-to-be-moved reciprocates between the first position and thesecond position without passing through the third position.
 10. Theimage forming apparatus according to claim 9, wherein when movingbetween the second position and the third position, said controllercontrols the drive of said motor so as to permit switching from thesecond position to the third position without passing through the firstposition and so as not to permit switching from the third position tothe second position without passing through the first position.
 11. Theimage forming apparatus according to claim 9, wherein when the imageformation is carried out at the second position, said controllercontrols said motor so that the member-to-be-moved is disposed at thefirst position at an end of the image formation.
 12. The image formingapparatus according to claim 11, wherein when the image formation iscarried out in a state in which the position of the member-to-be-movedis switched from the first position to the second position, saidcontroller controls said motor so that the position of themember-to-be-moved is switched from the first position to the secondposition without passing through the third position.
 13. The imageforming apparatus according to claim 11, wherein when the imageformation is carried out in a state in which the member-to-be-moved isdisposed at the third position, said image bearing member is detachablymountable to a main assembly of said image forming apparatus, andwherein when the position of the member-to-be-moved is switched from thefirst position to the third position, said controller controls the driveof said motor so that the position of the member-to-be-moved is switchedfrom the first position to the third position via the second position.14. The image forming apparatus according to claim 9, wherein themember-to-be-moved is movable toward and away from said image bearingmember and includes first and second transfer members each configured totransfer an image onto said image bearing member, wherein said firsttransfer member contacts said image bearing member when themember-to-be-moved is disposed at the first position and at the secondposition, and is spaced from said image bearing member when themember-to-be-moved is disposed at the third position, and wherein saidsecond transfer member contacts said image bearing member when themember-to-be-moved is disposed at the third position, and is spaced fromsaid image bearing member when the member-to-be-moved is disposed at thefirst position and at the second position.
 15. The image formingapparatus according to claim 9, wherein the member-to-be-moved ismovable toward and away from said image bearing member and includes atransfer member configured to transfer an image onto said image bearingmember, wherein when the member-to-be-moved is disposed at the firstposition, said transfer member contacts said image bearing member,wherein when the member-to-be-moved is disposed at the second position,said transfer member is disposed at a first spaced position where saidtransfer member is spaced from said image bearing member, and whereinwhen the member-to-be-moved is disposed at the first position, saidtransfer member is disposed at a second spaced position longer in spaceddistance between said transfer member and said image bearing member thanthe first spaced position.
 16. The image forming apparatus according toclaim 15, wherein when a reference pattern, which is not to betransferred onto a recording material during the image formation, isformed, said controller controls the drive of said motor so that theposition of the member-to-be-moved is switched from the first positionto the second position.